1. Field of the Invention
The present invention relates to a system of determining a position of a mobile device, and more particularly, to determining a position by using ultrasonic waves.
2. Related Art
Currently widely used positioning systems include a GPS (Global Positioning System) that covers a wide area using an artificial satellite. However, the GPS cannot be used indoors and it may not be operated in an area where buildings stand close together. Furthermore, although the GPS has good relative accuracy for a wide area, it has repetitive accuracy as low as several meters for a narrow area.
Korean Patent. No. 0351962, entitled ‘Navigation System using Pseudo-Satellite’, proposes a method of using the conventional positioning system indoors. However, this method is difficult to practically use because there is a large variation in signal intensity in a close range. Accordingly, a variety of techniques of using ultrasonic waves for positioning systems have been proposed.
FIG. 1 shows the Bat ultrasonic location system proposed as an active Bat system by AT&T Laboratories Cambridge. In this system, a mobile generates ultrasonic waves. The positioning method using ultrasonic waves is difficult to simultaneously transmit ultrasonic waves due to interference of ultrasonic waves, different from the method of using electric waves. Thus, the mobile generates an ultrasonic signal and a plurality of receivers measure arrival time of the ultrasonic signal.
Moreover, Korean Patent Publication No. 2003-009387, entitled ‘Ultrasonic sensor system for positioning mobiles’ proposes a method by which mobiles receive ultrasonic waves. According to this method, however, multiple mobiles cannot be independently operated because the mobiles transmit synchronization signals. Particularly, this method requires an additional rule because there is interference among the multiple mobiles.
Furthermore, U.S. Pat. No. 5,793,704, entitled ‘Method and Device for Ultrasonic Ranging’ discloses a ranging method using ultrasonic waves and maximum amplitude. However, this method is considerably complicated and performance-restrictive.